The removal of contaminants from aquifers has met with limited success. One method presently used to treat contaminated aquifers is a pump and treat process. In a pump and treat process, contaminated ground water is brought to the surface for treatment and returned to the aquifer. However, large amounts of contaminants remain adsorbed onto aquifer solids.
The contaminants adsorbed onto aquifer solids slowly leach into the aquifer, recontaminating the aquifer. Continuous treatment of the aquifer during the slow leaching process is costly and impractical.
The treatment of contaminants adsorbed onto aquifer solids in situ by remediation with microorganisms has been limited. Microorganisms introduced to a site by injection can migrate on their own or in response to natural or imposed hydrogeological gradients. Movement by diffusion is slow. Movement imposed by hydrogeological gradients is nonuniform and multidirectional.
The movement of microorganisms through the aquifer is often blocked by nonuniform aquifer physical structures or features. Natural hydrogeological gradients frequently do not run in the direction of the plume of the contamination.
Thus, in situ treatment of aquifer solids with microorganisms has been limited due to the low frequency of contact of the microorganism with the targeted contaminated surfaces.